Production of plural-phase alloys



United States Patent 3,296,695 PRODUCTION OF PLURAL-PHASE ALLGYS Allen 1S. McDonald, Samuel 0. Spooner, and Charles D. Coxe, Fairfield, Conn assignors to Handy & Harman, New York, .N.Y.., a corporation of .New York No Drawing. Filed Nov. 18,1963, Ser. No. 324,225 13 Claims. (Cl. 29-528) Thisinvention relates to the production of plural-phase alloys in wrought form, such for example as alloys comprising a hard and brittle phase disposed in a basis metal which is relatively workable and which maybe a single metal ora solid solution alloy or even an alloy of two or more phases. In accordance with the invention, such alloysareproduced by tightly wrapping one or more thin metallic sheets into a tight coil to form an extrusion billet,

andextruding such billetinto a coalesced shape.

Pluralwphase alloys of the character with which this invention isi concerned heretofore have generally been made by themethodst of powder metallurgy, because the hard and: brittle phase which they contain cannot generally be incorporated into wrought shapes by customary melting, casting and metal working practices. A few such alloys have also been made, by internally oxidizing alloys comprising a small quantity of easily oxidizable metal in a relatively largequantity of a metal which does not oxidize readilyq It has even been proposed to produce alloys of this, latter character. by extruding surface-oxidized chips, turnings, punch press, scrap, etc., either before or after heating to, enable the surface oxide to diffuse into the metal and internally oxidizethe alloy. All such methods minor proportion of another metal with an element capable of forming a non-metallic compound with said other metal until particles of such compound are formed and substantially uniformly dispersed throughout the matrix metal. The it resulting plural-phase alloy sheet then is coiled on itself to form a billet, the billet is heated to the extrusion temperature of the plural-phase alloy, and the heated billet istextruded to form a coalesced alloy.

Dispersion hardened alloys, such for example as internally oxidized dispersion hardened alloys are readily made in massive wrought form by the method of the in vention. To make such a product, a thin strip of oxidation hardenable alloy (that is, an alloy comprising a small quantity of a readily oxidizable metal the oxide of which hasta high heat of formation such as magnesium, beryllium; aluminum, or silicon, and a relatively large quantity of a metal which does not oxidize very readily, i.e. whose oxidehasa relatively low heat of formation, such for example asthe metals of groups Ibjl and VIII of the periodic table) is subjected to oxidation, then is coiled on itself in concentric 1=ayers-to form a cylindrical extrusion billet, is heated to extrusion temperature, and is extruded in the form of a coalesced shape.

Theinvention is described in greater detail below with respect to the production of internally oxidized dispersion hardened alloys. This description, however, is by way of example and does not denote the limits of useful application of, the method of the invention.

3,296,695 Patented Jan. 10, 1967 ice INTERNALLY OXIDIZED DISPERSION HARDENED ALLOYS The internal oxidation process functions by the diffusion of oxygen from the surface toward the interior of a solid solution alloy comprised of a major portion of solvent metal having a relatively low heat of oxide formation such as silver, copper, or nickel and a minor portion of solute metal having a relatively high heat of oxide formation such as Mg, Al, or Be, which metals are selectively oxidized to form highly dispersed, fine particles of oxide in the solvent matrix. Solid solutions of other metals than these examples may also be used provided that there is a substantial contrast in the oxide heats of formation of the solvent and solute metals, the solvent metal having lower heat formation and the capability of diffusing effective amounts of oxygen without itself becoming excessively oxidized. Such alloys, as noted above, are called oxidation hardenable alloys.

The internal oxidation process is the most effective method known for producing increased strength and hardness by the dispersion of oxide particles in the matrix or solvent metal. It is, however, effective only for small sizes of metal parts or particles, smaller than about 0.1, and preferably smaller than about 0.02 in thickness or diameter. Larger thicknesses require excessively long times for completion of the internal oxidation process, and the slower rate of oxidation results in coarser and less effective precipitated oxide particles in the interiors of the larger pieces. In order to produce larger sections of internally oxidized material, one may produce powders, chips, or other small particles of the solid solution alloy and then internally oxidize these particles, after which they may be compressed into a billet and coalesced by hot extrusion. This process has several shortcomings which the present invention overcomes. These shortcomings are:

(l) Unavoidable non-uniformity of powder or chip particle size results in non-uniformity of internal oxide particle size.

(2) When oxidation is accomplished by the two step process of first forming an oxide layer on the surface and then diffusing the oxygen of such layer into the powder or chip particle, the smaller particles will have an excessive amount of surface oxide and the larger particles will have a deficient amount of surface oxide when the average amount of surface oxide is in balance with the internal oxygen demand for material of a given composition and particle size.

(3) The poured density of powders or chips, when such particulate matter is placed into a can to form an extrusion billet, is low, often less than 50%, thus making inefficient use of extrusion container space. Prepressing can increase the packed density, but this requires an additional operation and heavy expensive equipment.

(4) It is very difficult to form uniform surface oxides on a large loose mass of particles. Those particles on the outside of the heap take more oxygen than those inside, and if tumbling is resorted to to equalize particle exposure, already formed oxides on the first exposed particles will be abraded away.

In accordance with this invention the aforementioned difficulties are overcome by first rolling the cast, solid solution alloy into a continuous strip, uniformly and suitably thin for effective and economically rapid internal oxidation. For this purpose the strip should be less than 0.1", and preferably less than 0.02, in thickness. This strip is then either directly internally oxidized, or is indirectly internally oxidized by first forming a surface oxide layer in an oxidizing environment and then diffusing inwardly the oxygen of such layers in an inert environment. The oxidized strip is then wrapped about a suitable mandrel to form a multilayer high density billet resembling a roll of paper. When a solid billet is desired, the mandrel may be a rod from a previous extrusion of the same alloy composition. When a tubular billet is desired, any removable mandrel may be used. This wrapped billet is then heated (either in a can or not) to extrusion temperature and extruded into a rod or tube. The extrusion ratio is preferably higher than 15 to 1 to assure complete coalescense of the multilayer billet.

Alternatively the surface oxidized strip may be Wrapped into billet form, and diffusion can be accomplished by heating the wrapped billet containing enclosed surface oxides. The temperature and time of heating depend on the particular alloy and the actual thickness of the strip employed, but should be selected to insure that the enclosed oxide will be quite completely dissociated and to allow its oxygen to diffuse throughout the metal. It will be understood that the thinner the strip, the less need be the amount of surface oxide and the shorter the diffusion time.

Also, higher temperatures shorten the necessary diffusion time.

Example I An alloy of 0.25% magnesium, balance silver, was melted and cast into a bar, and rolled into 10" wide strip .010" thick by conventional processes. The alloy strip was formed into an open spiral coil with about A" spacing between turns to allow free circulation of air or oxidizing gas between turns. This open coil, suitably supported on a heat resistant metal spider or carrier, was heated to 1350 F. in an air circulating furnace enriched with oxygen and was held at this temperature for /2 hour. Heating at such temperature and for such time was sufficient to oxidation harden, throughout, strip of this composition and thickness. The resulting internally oxidized strip was then wrapped around a mandrel of previously extruded rod, in diameter, of the same material. The wrapping was continued until a billet 3 A" in outside diameter and 10" long was formed. Such billet was 95% of theoretical density. The feed strip was cut off and the billet secured against unwrapping by a circumferential strap of wire of the same material. The wrapped billet containing the mandrel was transferred to a heating furnace, was heated in air to 1550 F. and then transferred to the extrusion container of an extrusion press, from which it was extruded under a force of 600 tons to A3" diameter rod. This rod was of sound, dense, completely, consolidated, hard metal having a tensile strength of 60,000 psi. and elongation of 18% in 2". Upon further cold drawing to .100" diameter, the properties were:

Ultimate tensile strength p.s.i. 80,000

Elongation in 2" percent 7 Yield strength (0.2% elongation) p.s.i. 70,000

Electrical conductivity percent IACS 75 Example II Example III An alloy of 0.1% beryllium, balance copper, was cast, rolled, and formed into an open coil as in Example I. The open coil was cleaned and pickled in acid and then was immersed in an alkaline oxidizing solution at 210 to 215 F. for 15 minutes, thereby producing an adherent, black copper oxide coating on each side of the coiled strip. The total oxygen content of the resulting coating was slightly in excess of that required to oxidize completely the beryllium contained in the strip to BeO. The oxide coated strip, still in the soft condition, was wrapped about a rod of previously extruded oxidation hardened beryllium copper and was placed in a copper can and sealed. The sealed billet was heated for 4 hours at 1750 F. to dissociate the copper oxide coating and diffuse the oxygen thereof into the strip, there to oxidize and precipitate the contained beryllium to form a separate phase of BeO. The heated and diffused billet was transferred directly to the extrusion press and was extruded under a force of 600 tons to %1" rod having 72,000 psi. tensile strength. On further cold drawing to .100" diameter, the tensile strength of the rod was increased to 93,000 psi.

In carrying out a process according to Example I, a continuous strip heating operation could be employed for the oxidizing step in place of batch heating of open coils.

In the process of Example III, an alkaline chemical oxidizing bath is used to facilitate obtaining a uniform, controllable amount of copper oxide on the strip. The oxide coating thus formed is, in contrast to heat-formed oxide scale, adherent and nonspalling and easily withstands the subsequent wrapping operation by which the coiled billet is formed. In practice, it is convenient and effective to determine first the weight of copper oxide to be deposited under the time-temperature conditions of the bath operation; second, the beryllium content of the alloy is carefully determined; and thirdly, the thickness of strip to be rolled can be calculated so that the amount of beryllium per unit area of strip will be approximately stoichiometrically equivalent to the oxygen in the coating per same unit area.

An alternative practice to that of Example III is to heat the beryllium copper strip either in the form of an open coil or in the form of a straight length in an environment that maintains a partial pressure of oxygen approximately equal to the dissociation pressure of Cu O, so as to diffuse oxygen into the strip without excessively oxidizing the copper. This may be accomplished, for instance, by heating the strip in a closed system containing C1120.

In yet another alternative practice to that of Example III, the strip may be first heated in an oxidizing environment to form a surface oxide scale, after which it is heated in a neutral environment for sufficient time to difiuse the oxygen of the scale into the metal to oxidize and precipitate the beryllium; and then preferably the strip is heated in a reducing atmosphere to eliminate excess oxide over that required to oxidize the beryllium.

In all cases where diffusion and hardening of the strip precedes coiling it into a billet by wrapping about a mandrel, somewhat more difiiculty will be encountered in wrapping the harder metal than in those cases where the strip is only surface oxidized before wrapping.

While the foregoing examples'and embodiments of the invention relate particularly to internally oxidized dispersion hardened alloys, it is evident that other products also may be made by the method of the invention. For example, an alloy composition containing a precipitated nitride phase may be made by diffusing nitrogen into a stri of nitridable composition, coiling the strip into a billet, and extruding it. Extruded shapes containing a precipitated carbide phase may be made by diffusing carbon into a thin strip of a suitable alloy, coiling the carburized strip into billet form, and extruding. Indeed, virtually any product that heretofore has been made by the powder metallurgy technique of interacting a metal powder with another component, whether gaseous, liquid or solid, and then consolidating, can be made by the method of this invention, and can be made to more exacting specifications and more uniformly by the method of the in- .vention because the ratio of surface area to mass of the metal strip can be closely controlled and can be held uniform throughout the billet.

We claim:

1. The method of producing a wrought plural-phase alloy which comprises the steps of reacting, at an elevated temperature, a sheet of a solid solution alloy comprising major proportion of a matrix metal and a minor pro- 1 capable of; forming a non-metallic compound with said other metal; until particles of said compound are formed and. substantially uniformly dispersed as a separate phase throughout said matrix metal, coiling the resulting pluralphase, alloy sheet on itself to form a billet, heating the coiledqsheet billet to the extrusion temperature of the l plural-phase alloy, and extruding the heated billet to form t a coalesced extruded shape.

2.11 The method according to claim 1, characterized in that the extruded shape is heated to an elevated diffusion temperature to promote more complete interaction of the elements forming said non-metallic compound.

3. The method according to claim 1 characterized in that the extruded shape is worked to smaller cross sectional area and the worked'product is heated *to an elevated: diffusion temperature to promote more complete interaction of the elements forming said non-metallic compound. 1

4. The method according to claim 1, characterized in that the non-metallic element is selected from the group consisting of oxygen, nitrogen and carbon.

, 5. The method according to claim 1, characterized in that a gaseous non-metallic element is reacted with the solid solution alloy sheet.

6. The method of forming a wrought shape of an internally oxidized alloy which comprises the steps of reactingflwith an oxidizing agent a sheet of a solid solution alloy comprising a major proportion of a matrix metalvand: a minor proportion of a relatively more easily oxidized metal to form an internally oxidized alloy sheet in which particles of an oxide of the more easily oxidized metal are dispersed throughout ,a matrix of the matrix metal, coiling. the resulting internally oxidized sheet on itself to form a billet, heating the billet to the extrusion temperature, of, the internally oxidized alloy, and extrud- 1 ing the heated billet to form a coalesced extruded shape.

11. The method according to claim 6, characterized in that the matrix metal is a metal selected from groups Ib and VIII of the periodic table, and the more easily oxidized metal is selected from the group consisting of magnesium, aluminum, beryllium and silicon.

12. The method of forming a wrought shape of an internally oxidized alloy which comprising the steps of reacting with gaseous oxygen at an elevated temperature a thin sheet of a solid solution alloy comprising a major proportion of a matrix metal and a minor proportion of a relatively more easily oxidized metal to form an internally oxidized alloy sheet in which particles of an oxide of the more easily oxidized metal are substantially uniformly dispersed throughout a matrix of the matrix metal, tightly coiling the resulting oxidized sheet on itself in con* centric layers to form a high densityscylindrical extrusion n billet, heating said billet to the extrusion temperature of the internally oxidized alloy, and extruding the billet to form a coalesced extruded shape.

13. The method of forming a wrought shape of an internally oxidized alloy which comprises the steps of reacting with an oxidizing solution a thin sheet of a solid solution alloy comprising a major proportion of a matrix metal and a minor proportion of a relatively more easily oxidized metal to form a surface-oxidized alloy sheet, drying and heating the surface-oxidized sheet until particles of an oxide of the more easily oxidized metal are substantially uniformly dispersed throughout the sheet in a matrix of the matrix metal, tightly coiling the resulting internally oxidized alloy sheet on itself in concentric layers to form a high density cylindrical extrusion billet, heating said billet to the extrusion temperature of the internally oxidized alloy, and extruding the billet to form a coalesced extruded shape.

References Cited by the Examiner UNITED STATES PATENTS 2,261,436 11/1941 Fooger 29528 2,913,813 11/1959 Homer et al. 29194 3,113,376 10/1963 Pfiumm et al 29155.5 3,140,172 7/1964 Coad 29-528 X 3,181,936 5/1965 Denny et al 29-494 3,218,693 1l/1965 Allen et al 29155.5

JOHN F. CAMPBELL, Primary Examiner.

P. M. COHEN, Assistant Examiner. 

1. THE METHOD OF PRODUCING A WROUGHT PLURAL-PHASE ALLOY WHICH COMPRISES THE STEPS OF REACTING, AT AN ELEVATD TEMPERATURE, A SHEET OF A SOLID SOLUTION ALLOY COMPRISING A MAJOR PROPORTION OF A MATRIX METAL AND A MINOR PROPORTION OF ANOTHER METAL, WITH A NON-METALLIC ELEMENT CAPABLE OF FORMING A NON-METALLIC COMPOUND WITH SAID OTHER METAL, UNTIL PARTICLES OF SAID COMPOUND ARE FORMED AND SUBSTANTIALLY UNIFORMLY DISPERSED AS A SEPERATE PHASE THROUGHOUT SAID MATRIX METAL, COILING THE RESULTING PLURALPHASE ALLOY SHEET ON ITSELF TO FORM A BILLET, HEATING THE COILED SHEET BILLET TO THE EXTRUSION TEMPERATURE OF THE PLURAL-PHASE ALLOY, AND EXTRUDING THE HEATED BILLET TO FORM A COLAESCED EXTRUDED SHAPE. 